Bending Properties of Lightweight Copper Specimens with Different Infill Patterns Produced by Material Extrusion Additive Manufacturing, Solvent Debinding and Sintering

Material extrusion additive manufacturing (MEX) is a versatile technology for producing complex specimens of polymers, ceramics and metals. Highly-filled filaments composed of a binder system and a high-volume content of sinterable powders are needed to produce ceramic or metal parts. After shaping the parts via MEX, the binder is removed and the specimens are sintered to obtain a dense part of the sintered filler particles. In this article, the applicability of this additive manufacturing process to produce copper specimens is demonstrated. The particular emphasis is on investigating the production of lightweight specimens that retain mechanical properties without increasing their weight. The effect of infill grades and the cover presence on the debinding process and the flexural properties of the sintered parts was studied. It was observed that covers could provide the same flexural strength with a maximum weight reduction of approximately 23%. However, a cover on specimens with less than 100% infill significantly slows down the debinding process. The results demonstrate the applicability of MEX to produce lightweight copper specimens.

Presintered Titanium-Hydroxyapatite Composite Fabricated via PIM Route

Ti6Al4V-HA composites have been recognized for their potential for biomedical implantation purposes. In the present study, Ti6Al4V-HA composites were fabricated by Powder Injection Molding (PIM) route. Ti6Al4V-HA feedstock at a ratio of 87:13 vol.% was prepared by using a binder system consisting of palm stearin (PS) and polyethylene (PE). The Critical Powder Volume Percentage (CPVP) value for Ti6Al4V-HA was 68 vol.%. Ti6Al4V-HA feedstock was developed at 66 vol.% powder loading. Ti6Al4V-HA feedstock showed pseudoplastic behaviour with a low viscosity and low activation energy of flow and was successfully injected into a tensile bar shape. The debinding process involved a solvent and thermal debinding operation. The debonded parts were sintered at 1300 °C, and the influence of the presintering stage on the physical and mechanical properties of the sintered parts was investigated. It was proven that the presintering stage was able to restrain the transformation of Ti6Al4V into Ti3Al (α2) as well as the decomposition of HA. These are key findings ideas for the designing of sintering parameters, where the decomposition of HA becoming the main problem in the sintering of Ti6Al4V-HA composites at a high temperature. The obtained results also showed that the sintered parts had a porous structure, which looked promising for their use in biomedical implantations. purposes.

Mechanism of Void Formation during Brazing of Ni Paste Brazing Filler Metal

Automobiles are equipped with EGR (Exhaust Gas Recirculation) coolers to improve fuel economy and exhaust gas suppression performance. Inside the EGR cooler, the moisture in the gas is condensed by cooling the hot exhaust gas. This condensed water is highly corrosive because sulfur oxides dissolve. Therefore, stainless steel and Ni-based brazing metal having excellent corrosion resistance are used for the EGR cooler.Until now, stainless steel has been brazed under a vacuum atmosphere. However, there are increasing opportunities to braze stainless steel in an inert atmosphere gas at atmosphere for cost reduction and mass production. In this case, a paste-type brazing filler metal consisted of a powder brazing filler metal and a binder is used. As is well known, a debinding process that volatilizes the binder is needed. From previous research in this laboratory, it is clarified that the binder causes voids. In addition, it is said that the size and location of voids generated at the brazed joint affect the product performance. On the other hand, the detailed investigation about the influence which the installation position of a paste type brazing filler metal on the void formation process has not yet been made. Therefore, in this study, the arrangement method and influence on heating rate and debinder temperature on void formation were investigated by X-ray CT.

Investigating the relation between debinding atmosphere and mechanical properties of stereolithography-based three-dimensional printed Al2O3 ceramic

Ceramic green bodies fabricated by stereolithography-based three-dimensional printing technology often have high loading of ultraviolet curable resins, which produce undesirable phenomena such as cracking, deformation, and blistering during the debinding process. Results showed that compared to argon and vacuum, air atmosphere provided higher flexural strength owing to the elevated density. The differences in microstructure between specimens prepared under these atmospheres were attributed to exothermic oxidation reactions occurred under air when compared to endothermic pyrolysis reactions under vacuum and argon. The debinding atmosphere showed little effect on crystallite size due to the elevated sintering temperature, which would determine the final crystallite size of Al2O3. Debinding under air atmosphere resulted in flexural strength of 176.69 MPa and open porosity of 23.4%. The flexural strength of the ceramics debinded in air was 21.6% higher than the ceramics debinded in argon atmosphere.

Manufacturing complex Al2O3 ceramic structures using consumer-grade fused deposition modelling printers

Purpose This study aims to fabricate complex ceramic tetrahedron structures, which are challenging to produce by more conventional methods such as injection molding. To achieve this aim, thermoplastic-ceramic composite filaments were developed and printed with unmodified, consumer-grade, fused deposition modelling (FDM) printers instead. Design/methodology/approach Al2O3 ceramic powder was mixed with ethylene vinyl acetate polymer as a binder (50 Vol.- per cent) to form a filament with a constant diameter of 1.75 mm. After the printing and thermal treatment stages, the shrinkage and mechanical properties of cuboid and tetrahedron structures were investigated. Findings The shrinkage of the parts was found to be anisotropic, depending on the orientation of the printing pattern, with an increase of 2.4 per cent in the (vertical) printing direction compared to the (horizontal) printing layer direction. The alignment of the ceramic particle orientations introduced by FDM printing was identified as a potential cause of the anisotropy. This study further demonstrates that using a powder bed during the thermal debinding process yields sintered structures that can withstand twice the compressive force. Originality/value Ceramic FDM had previously been used primarily for simple scaffold structures. In this study, the applicability of ceramic FDM was extended from simple scaffolds to more complex geometries such as hollow tetrahedra. The structures produced in this study contain dense parts printed from multiple contiguous layers, as compared to the open structures usually found in scaffolds. The mechanical properties of the complex ceramic parts made by using this FDM technique were also subjected to investigation.